Fiber Bragg grating (FBG) sensors have been extensively utilized in structural health monitoring (SHM) due to some significant advantages such as lightweight, small size, and high temperature tolerance. However, when working under extreme conditions, FBG sensors are prone to chirped reflection spectrum that leads to strain reading anomalies (SRAs). These chirped phenomena such as peak broadening, peak reduction, and multiple peaks should be tackled first, otherwise the accuracy and reliability of the sensors be compromised significantly. This paper proposes an adaptive post-processing method to efficiently detect and remove SRAs caused by the chirped reflection spectrum in FBG sensors. The proposed method utilizes the K-means clustering algorithm to determine adaptively thresholds instead of relying on manual fixed thresholds. Furthermore, a geometric threshold offset method is applied to distorted strain curves to eliminate SRAs. The effectiveness of the proposed method is evaluated using the Pearson correlation coefficient. This index can characterize the correlation between the post-processing strain curve and the temperature/pressurized curve. The experimental results of a 3.35-meter-diameter composite tank under a cryogenic pressurization test are processed by the proposed method and two other existing methods. The comparisons illustrate the superiority of the proposed method.

Objective Distributed optic fiber sensor(DOFS)is widely used for status monitoring and damage detection of aerospace vehicles due to its ability to achieve large-area and high-density sensing of structures.However,in the face of uncertainties caused by the harsh service environment of aerospace,a phenomenon of strain reading anomalies(SRAs)occurs in DOFS measurements.These SRAs result in significant strain peaks occurring in localized regions or at specific moments in time,thereby posing challenges for DOFS to accurately measure physical quantities and making it even more difficult to interpret these measurements.To minimize the negative effects of SRAs,some researchers have adopted a series of data processing methods,such as polynomial fitting method,spectral shift quality(SSQ)method,geometrical threshold method(GTM),and polynomial interpolation comparison method(PICM).Although these data processing methods are effective in reducing random errors in measurement data,they fail to completely remove the phenomenon of SRAs,and there is still a risk of removing highly reliable measurement readings.Meanwhile,the above methods still use the fixed threshold method to detect and determine the anomalies,and the determination of the fixed threshold relies on manual experience,which has low detection efficiency and a high false alarm rate,thus limiting its application in complex service environments.Therefore,we propose an intelligent adaptive post processing method for detecting and quickly removing SRAs from DOFS. Methods The proposed algorithm,namely the adaptive geometrical threshold offset method(AGTOM),adopts the K-means clustering method to adaptively determine thresholds for distinguishing differences of thresholds caused by various structural features and service conditions.A continuous geometric correction is implemented on the distorted strain curves to effectively eliminate SRAs.To verify the effectiveness of the proposed method,a case study is conducted on the processing of DOFS measurement data collected during the pressure cycling test of a fuel tank.The Pearson correlation coefficient(PCC)is utilized to evaluate the correlation between the post-processing curves and normal strain curves.Besides,a comparison is conducted with other post-processing algorithms(GTM and PICM)to highlight the advantages of the proposed method. Results and Discussions Based on their different response characteristics,SRAs can be classified into two categories:harmless strain reading anomalies(HL-SRAs)and harmful strain reading anomalies(HF-SRAs).For the HL-SRAs,AGTOM consistently yields optimal post-processing results with PCC values not less than 0.965.It is followed by GTM,whose PCC values are all not less than 0.798.However,GTM interferes when HL-SRAs are coupled with NaN values.In addition,PICM achieves promising processing results only in the first typical case(i.e.,sparsely distributed HL-SRAs).In the remaining three typical cases,PICM still produces distortions with a PCC value not greater than 0.512.Importantly,both GTM and PICM exhibit distorted post-processing curves when HL-SRAs are coupled with NaN values.For HF-SRAs,AGTOM also yields the highest post-processing results,with no PCC value lower than 0.917.The susceptibility of PICM to curve distortion accurately reflects the difference between HF-SRAs and HL-SRAs because the main characteristic of the former is that strain values follow an erroneous strain response or frequent sudden changes.It is difficult to determine the change in strain increment using PICM because it detects and removes SRAs by comparing the fitted value with the original value.Compared with PICM,GTM takes into account the sudden changes of the strain increment,resulting in improved post-processing results when HF-SRAs consist of densely changed SRAs.However,similar to HL-SRAs,both GTM and PICM show worsened post-processing results when NaN values interfere with HF-SRAs,indicating lower algorithmic robustness for GTM and PICM compared to AGTOM Conclusions The proposed algorithm AGTOM is able to distinguish the differences in thresholds due to different structural characteristics and service environments.The K-mean clustering algorithm uses an internal evaluation metric,namely Davies-Bouldin index(DBI),to characterize the clustering effect of strain increments.The threshold is determined by obtaining the optimal k value.For the HL-SRAs,both GTM and AGTOM methods can achieve satisfactory processing results.However,PICM is susceptible to interference when facing densely distributed and coupled HL-SRAs,leading to serious distortions in its post-processing curves.For HF-SRA,the post-processing curves of the other two algorithms are distorted to varying degrees,except for AGTOM,which exhibits the highest PCC compared to the normal strain curve.For both HL-SRAs and HF-SRAs,GTM and PICM are interfered with when SRAs are coupled with NaN,indicating that the algorithmic robustness of both is lower than that of AGTOM.To further validate the effectiveness of AGTOM,it will still be necessary to test AGTOM by applying it to different experimental scenarios in the future.

The 8 mm-thick 2195 Al-Li alloy joints were achieved by Friction Stir Welding (FSW). The microstructural evolution, temperature-dependent mechanical properties, and fracture properties were studied. The T1, δ′/β′ and θ′ precipitates were observed in the Base Metal (BM) and the Heat Affected Zone (HAZ). Most of the precipitates, except for re-precipitated δ′/β′ phases, were dissolved in the Nugget Zone (NZ). The tensile specimens that failed at cryogenic temperatures (–196 °C) had the maximum Ultimate Tensile Strength (UTS), and the fracture surface showed the inter-granular fracture characteristics. Compared to those at room temperature (25 °C), the decreasing tensile properties at high temperature (180 °C) were related to microstructure and strain hardening effects. The NZ presented the optimal fracture toughness, and the Crack Tip Opening Displacement (CTOD) was mutually dominated by microhardness and grain size. Analysis on Fatigue Crack Growth (FCG) rates indicates that the Thermal-Mechanically Affected Zone (TMAZ) exhibited the most superior fatigue resistance performance at stress intensity range below 17 MPa·m1/2 due to compressive residual stress and the crack closure effect. The fatigue fracture surfaces reveal that the crack propagation zone was characterized by the striations and secondary cracks. Also, inter-granular fracture behavior was responsible for the fastest FCG rates in the NZ.

近每来,随着航天技术的不断进步及商业航天产业的长足发展,高经济性、高可靠性、多功能化的航天运载器成为航天技术发展的重要方向之一,而航天运载器机构技术的突破及发展是推动航天运载器技术进步,满足更丰富、更高要求的航天运载需求的重要基础之一.本文对航天运载器机构的发展进行阐释,对航天运载器机构的主要功能及性能需求进行综述,分析其面临的挑战,并对航天运载器机构技术未来的发展方向进行展望.

通过在运载火箭级间段增设栅格舵气动控制机构,能够在一二级分离后对一子级的姿态进行气动力控制,提高其落点精度,从而提高运载火箭内陆发射的落区安全性.按照动作时序,栅格舵机构需完成连接解锁-展开锁定-传动传力的动作功能,并承受火箭上升段和返回段的力、热载荷.对用于运载火箭落区控制的栅格舵机构技术路线进行阐述,形成栅格舵结构设计—载荷判别计算—机构构型设计—关键零组件设计—试验验证的栅格舵机构设计及验证的研制脉络,提出组合可调式的展开锁定机构设计方法,最后对用于运载火箭落区控制及重复使用的栅格舵机构设计提出技术发展建议.

针对运载火箭结构价格昂贵,通过试验获取强度变差系数困难问题,提出了基于产品实测数据仿真预估强度变差系数方法.以轴压载荷作用下的1 m直径薄壁正交网格加筋圆柱壳试验件为对象,开展了实现技术途径及试验验证研究.测量并统计试验产品材料性能、结构尺寸及几何形貌不确定性;应用双重傅立叶级数对实测几何形貌表征,将其引入到结构理想有限元分析模型,实现极限强度精确仿真分析;采用混沌多项式展开(Polynomial Chaos Expansion,PCE)代理模型,实现考虑关键参数不确定性的极限强度高效模拟打靶和强度总体变差系数预估;并开展了 3个试验件的轴压强度破坏试验验证.结果表明,预估的强度变差系数可很好包络试验样本变差系数,具有较高可靠性的同时,相对历史统计数据有较大降低,对实现结构可靠性安全系数的精确量化设计,挖掘现代先进结构承载潜力有重要意义.

为有效缩短箭体长度,增大喷管扩张比,提高发动机比冲,对运载火箭发动机进行了喷管变形机构型综合分析.首先分析了国内外喷管变形机构发展历程,在此基础上系统总结了喷管变形机构的典型应用,并对典型喷管变形机构进行了方案分析,研究了其组成原理和功能设计特点,最后基于机构拓扑图分析方法给出机构构型方案及设计方法.介绍了国内外相关喷管变形机构各构型方案运动原理及设计特点,并综合分析评价了各方案,提出了喷管变形机构技术发展建议,可为运载火箭发动机变形机构设计提供支撑.

The launch vehicle separation technology at home and abroad is systematically studied, including booster separation, interstage separation, fairing separation and payload separation. Combined with the technical development needs of non-pyrotechnic separation mechanism, the technology of separation mechanism is comprehensively analyzed from two aspects of the connection form and driving energy. The technical characteristics of each mechanism are compared and analyzed, and the development trend of non-pyrotechnic separation mechanism product is researched and prospected, aiming at providing reference for the technological innovation and product systemic development of non-pyrotechnic separation mechanisms of launch vehicle.

复合材料贮箱作为未来航天运载动力系统的关键部件,其结构的状态监测与性能评价是保证航天器安全运行的关键问题之一.声发射作为一种新型动态无损检测/监测技术为复合材料贮箱结构性能监测提供了一种行之有效的技术手段.本文以复合材料贮箱为背景,首先介绍了复合材料贮箱的失效模式及常见的健康评价技术;其次介绍了声发射检测技术的基本原理,并综述了声发射技术在复合材料贮箱损伤表征上的应用研究现状,最后讨论了声发射技术应用于复合材料贮箱的发展趋势及面临的挑战.

Creep aging forming (CAF) is a potential process to manufacture large integral components of Al–Li alloys, which exhibits poor formability and susceptibility to damage and cracking via traditional plastic forming processes. Al–Li alloys also have disadvantages, such as low creep and comprehensive properties.To address this problem, this study adopted pre-aging as a treatment process before creep aging (CA). The effects of pre-aging at different temperatures (65 °C, 90 °C, and 115 °C) on the CA of Al–Li alloys were evaluated at 155 °C for 18 h. Creep strain, the evolution of mechanical properties, and the microstructural characteristics were investigated as well. The results showed that pre-aging could effectively influence the subsequent CA behavior. As the pre-aging temperature increased, creep strain accumulation during CA decreased. Meanwhile, pre-aging significantly increased the elongation (EL) of the specimens after CA; Notably, the increase in EL did not compromise strength. Changes in the microstructure of the specimens after pre-aging and CA tests were observed by transmission electron microscopy. The effect of pre-aging on the subsequent CA properties mainly revealed that the strength was not lower than that of the specimen without pre-aging after the same CA test through adjusting the percentage and size of the T1 and θ′ phases. In addition, pre-aging could promote the transformation of the fracture mechanism from intergranular fracture to mixed fracture in the specimen after CA.

Homogenization treatment is vital for eliminating eutectic structure and ensuring a preferable microstructure foundation for Aluminum Lithium (Al-Li) alloys. In this paper, solidification phases in an as-cast Al-Li alloy were revealed and their evolutions during multiple homogenization processes were analyzed by means of scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and differential scanning calorimetry (DSC) analysis. The results showed that the as-cast microstructure mainly contained needlelike Al2CuLi and Al2Cu phase, large size Cu-rich phases and netlike Ag-containing phases attached to them. As the alloy homogenized by 455°C/16h, except for needle-like phases inside grains, part of phases on grain boundaries had dissolved into the matrix and exhibited rounded shapes. As homogenized by 455°C/16h+495°C/16h, Ag-containing phase had completely dissolved into the matrix while the Cu-rich phases remained and showed two different morphologies depending on whether Mg element was contained. Prolonging the second homogenization time to 28h, no obvious change occurred for the Cu-rich phase. As homogenized by 455°C/16h+495°C/20h+512°C/20h, most Cu-rich phase had dissolved into the matrix while residual phase was mainly Fe-containing phase. This proposes an effective way to eliminate various solidification phases in Al-Li alloys and identify their contents.

产品化是实现运载火箭箭体结构"高质量、高效率、高效益"发展的有效举措.贮箱结构是箭体结构的重要组成部分,本文以此为切入点,分析贮箱结构特点和产品现状,提出了"架构—平台—型谱—货架"的贮箱结构产品化思路和"主结构平台化,零组件货架化,货架数字化"的产品发展理念,在贮箱φ2.25m、φ3.35m模块平台建设和零组件货架建设两方面进行了成功实践,为运载火箭结构产业布局及其他产品化工作提供思路.

火工分离装置在爆炸分离过程中产生的高频、强瞬态爆炸冲击,给航天运载火箭内部的设备带来恶劣的影响,是航天运载火箭研制过程中必须考虑的问题.通过研究以分离螺母装置为代表的点式分离装置、以扁平管-凹槽板装置为代表的线式分离装置的爆炸冲击产生过程,利用仿真预示和试验评价相结合的方法,获得了两类典型分离装置的爆炸冲击产生原因,并针对性地提出了冲击抑制措施.通过研究发现,优化分离螺母装置的进气通道结构、内部撞击吸能结构和连接固定结构,能够将分离螺母装置产生的爆炸冲击降低50％以上.通过分析扁平管-凹槽板分离装置爆炸冲击产生原因,发现其主要由分离过程扁平管与端框的结构碰撞和分离板断裂应力产生,通过增加减振框和在扁平管与上下端框之间采取隔振的降冲击措施能够在一定程度上降低分离冲击水平.

为解决航天火工装置中常用高强钢存在易氢脆、裂纹敏感等问题,研究了回火温度分别为540℃及595℃2种热处理制度下PH13-8Mo沉淀硬化不锈钢的力学性能和抗爆炸冲击能力.测试发现回火温度540℃状态的PH13-8Mo钢具有较高的强度和较好的冲击韧性,能够代替30CrMniA或者30CrMnSiNi2A等常用高强钢材料.回火温度595℃状态的PH13-8Mo钢强度相对于回火温度540℃状态有所降低,但冲击韧性进一步提高,具有优异的抗爆炸冲击能力,适用于爆炸冲击防护要求高、承载能力要求相对较低的环节.

评价了2219-CS铝合金FSW和TIG焊接头的力学性能,并采用晶间腐蚀、剥落腐蚀及电化学腐蚀方法对2219-CS铝合金FSW和TIG焊接头进行了整体及分区域腐蚀行为表征,借助光学显微镜和扫描电子显微镜分析了表面腐蚀形貌.结果表明,搅拌摩擦焊接头焊核区的细晶结构和弥散再分布的沉淀相大幅度提高了其耐腐蚀性能,热影响区中沉淀相回溶及粗化较TIG焊接头热影响区较弱,耐腐蚀性能有一定提高,搅拌摩擦焊接头的高电化学均质性宏观表现为其整体腐蚀速率的显著降低.

In this study, a two-stage creep aging (CA) is established by adding a new stage of low-temperature CA to the traditional single-stage CA. The results show that the two-stage CA can effectively increase the elongation (EL) of the material by about 39.2% without sacrificing strength and creep strain. In the first stage of two-stage CA, as temperature increases, EL improvement first increases and then decreases; when the temperature varies between 65 ? and 115 ?, total creep strain remains consistent. Observation of the microstructures of the specimens under different CA processes reveals that two-stage CA mainly affects the mechanical properties of the material by adjusting the properties of the GP zones inside the material in the first stage of two-stage CA, which further affects the number and size of the T-1 phase in the subsequent CA process. Whether the GP zones evolve into a large number of T-1 and theta ' phases in the first stage of two-stage CA can directly influence the creep strain of the entire two-stage CA process and changes in the EL of the material after CA.

The composite tank has become the trend and focus for the power system of the new generation aerospace vehicles. However, the evaluation methods and monitoring technologies for composite tanks under cryogenic experiments are still challenging problems. In this paper, fiber Bragg grating (FBG) is used to measure the strain and temperature of the stiffened composite tank under room and cryogenic temperature pressurization experiments. Temperature compensation based on the thermal stratification phenomenon is proposed to increase the reliability and accuracy of strain monitoring in cryogenic environment. A non-linear fitting based calibration method of temperature sensitivity coefficient addresses the non-linear relationship between the FBG wavelength and temperature change from liquid nitrogen temperature to room temperature. The results show that the average absolute error of the nonlinear calibration method in the cryogenic test is less than 50 με. It is also illustrated that the structural features of the sensor location can be qualitatively determined according to the strain changes of different sensors. The comparison of strain increments in the cyclic pressurization illustrated that the different performance degradation phenomena of different regions could be observed. These results provide strong support for the high stability and reliability of FBG-based composite tank strain monitoring.

在航天领域,执行分离任务的装置根据触发方式可分为火工和非火工两大类,其中非火工分离装置由于其可控、低冲击、可重复测试和使用等特点,是未来航天分离设计的趋势.本文介绍了一种新型非火工分离原理样机,详述了该装置的工作原理,并对其主要性能进行了系统性的表征和分析.

系统地概括了低温贮箱用复合材料的研究背景、进展动态及研究现状,重点介绍了复合材料低温贮箱成型工艺、复合材料与低温推进剂之间的安全性及复合材料自身的低温力学性能.研究表明:自动铺丝成型工艺推动了无内衬的复合材料低温贮箱的发展;在冷热循环作用下界面等薄弱区域萌生大量微裂纹,机械载荷促进下形成低温推进剂泄漏路径;开发满足液氧相容性要求、工艺要求和力学性能优异的环氧树脂,是发展液氧贮箱用复合材料体系的关键;研究冷热循环作用和改性方法对于复合材料力学性能的影响,对可重复使用航天器复合材料低温贮箱应用的意义重大.

In this study, a radius expansion approach to enlarge radius around welding area is proposed to reduce residual stresses and distortion for large girth joint structure. The finite element (FE) model is developed to investigate the effects of expansion on the welding residual stresses and distortion. The simulation is verified with the experiment results. With larger radius expansion, there is lower residual stresses and distortion in joint. The mechanism is discussed using thermal-elastic-plastic (TEP) strains theory of welding. The theoretical analysis reveals that elastic strain induced by radius expansion is the key factor that reduces hoop residual stress and radial shrinkage.